Light-induced complex formation of bacteriophytochrome RpBphP1 and gene repressor RpPpsR2 probed by SAXS.

ABSTRACT: Bacteriophytochrome proteins (BphPs) are molecular light switches that enable organisms to adapt to changing light conditions through the control of gene expression. Canonical type 1 BphPs have histidine kinase output domains, but type 3 RpBphP1, in the bacterium Rhodopseudomonas palustris (Rps. palustris), has a C terminal PAS9 domain and a two-helix output sensor (HOS) domain. Type 1 BphPs form head-to-head parallel dimers; however, the crystal structure of RpBphP1?HOS, which does not contain the HOS domain, revealed pseudo anti-parallel dimers. HOS domains are homologs of Dhp dimerization domains in type 1 BphPs. We show, by applying the small angle X-ray scattering (SAXS) technique on full-length RpBphP1, that HOS domains fulfill a similar role in the formation of parallel dimers. On illumination with far-red light, RpBphP1 forms a complex with gene repressor RpPpsR2 through light-induced structural changes in its HOS domains. An RpBphP1:RpPpsR2 complex is formed in the molecular ratio of 2 : 1 such that one RpBphP1 dimer binds one RpPpsR2 monomer. Molecular dimers have been modeled with Pfr and Pr SAXS data, suggesting that, in the Pfr state, stable dimeric four ?-helix bundles are formed between HOS domains, rendering RpBphP1functionally inert. On illumination with light of 760 nm wavelength, four ?-helix bundles formed by HOS dimers are disrupted, rendering helices available for binding with RpPpsR2.

SUBMITTER: Papiz MZ 

PROVIDER: S-EPMC6899989 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature